DESCRIPTION (Investigator's Abstract): The application describes two areas of research, with a heavier emphasis on the first area than the second. The first area is an extension of previous studies that are directed at defining the stimulus characteristics that govern performance in simultaneous masking. The primary issue is the identification of processes that account for differences that occur when signals are placed at various temporal locations in a masker (overshoot). These mechanisms have been discussed for at least 25 years. Recent work, much of it published by the principal investigator, indicates that several mechanisms may be involved. Continuation of this work should reveal the relative contributions of these mechanisms, and perhaps more importantly, explore interactions among these basic auditory processes that may be important in understanding dynamic processing in general.